The impact of the growing cruise ship industry on air quality levels was investigated at the port of Copenhagen, Denmark. In 2018, 345 cruise ships visited Copenhagen, emitting 291 tons of NOx near the city centre. A spatiotemporal cruise ship emission inventory was developed for 2018 based on port list information, engine data, main and auxiliary engine power functions, and NOx emission factors, and was implemented in the OML-Multi atmospheric dispersion model. Evident plume effects from the cruise ships, which were traced by introducing the concept of likely concentration contribution, were obtained in the modelled and measured concentrations at Langelinie Quay, which is the busiest cruise ship terminal in Copenhagen port. Hourly peak values of NOx well above 200 μg m−3 were obtained at the top of a residential building at Langelinie Quay. The emissions from cruise ships were increasing the annual concentration of NO2 in the port area by up to 31% at ground level, and 86% 50 m above the ground in comparison to the urban background level. No exceedance of the European annual limit value of NO2 was obtained. The short-term impact of cruise ships was more pronounced with local exceedances of the hourly European limit value for NO2. Increasing cruise ship activity in Copenhagen port leads to air quality deterioration on short time scales with implications for human health.